It is common practice for governmental agencies to regulate access to territorial borders. It is also common for businesses and organizations to control access to portions of business property such as research and development areas, controlled areas such as flight line access, airports, seaports, vendor-only areas in trade shows, and many other locations. Organizations control access using a variety of methods, including gated entry, video surveillance, etc., together with identification cards such as passports, visas, birth certificates, social security cards, license numbers, and employee identification cards. For example, an organization may require an employee to present his or her card to security personnel at facility entrances to be permitted access to the facility.
Radio Frequency Identification (RFID) systems are increasingly being used to automate access to controlled areas. RFID systems include personal cards are encoded with a unique identification number. An identification apparatus such as a transponder communicates with the card to obtain the card's unique identification number, authenticate the card, and to grant/deny the card user access to a controlled area. RFID systems are also used to track inventory, typically using RFID tags affixed to boxed items, product surfaces, etc.
Most RFID systems operate at a very low frequency, which limits RFID detection to within a few inches between the card and the identification apparatus. However, some RFID systems, such as those which operate at ultra-high Frequency (UHF) bands, have considerably longer ranges, for example, tens of feet between the RFID card and the identification apparatus.
One problem with UHF RFID is that a card user or tagged entity can partially absorb and detune the RF electromagnetic energy required for RFID detection. One possible solution is to require the RFID card user to properly present the card in close proximity to the identification apparatus, for example, by contacting the card with a wall-mounted transponder. However, RFID card users often fail to properly present the card, resulting in degradation of RFID performance. In many instances, the card may be obscured, for example, in a pocket, purse, or wallet, causing RFID card blockage and detection failure. An RFID tag may be obscured by surfaces of the tracked inventory, for example, a metallic surface, resulting in RFID tag blockage and detection failure.
FIGS. 6 and 7 illustrate conventional UHF RFID card designs which suffer from poor detectability when the RFID card user fails to properly present the card to the detection apparatus. FIG. 6 illustrates a conventional RFID card having a simple single-port microchip RFID inlay 600, which includes a UHF antenna 604 and a one-port microchip 602. The RFID card suffers significant RF signal degradation when the user's hand obscures a portion of the antenna 604.
FIG. 7 illustrates a conventional RFID card having a RFID inlay 700 with a two-port microchip 702 and two UHF antennas 704, 706 coupled to the two-port microchip 702. The RFID inlay 700 alleviates the degradation problem with the single antenna inlay 600 by providing a second antenna 706 insulated from a first antenna 704. Thus, when the RFID card user's hand obscures one antenna, detection is maintained via the other antenna. However, in some instances, the user's hand can obscure the first and second antennas 704, 706, causing detection failures. Also, the conventional two antenna inlay 700 does not resolve detection problems when the user places the RFID card in a pocket, purse, or wallet.